High-strength zirconia-alumina composite ceramic substrate applied to semiconductor device and manufacturing method thereof

ABSTRACT

A high-strength zirconia-alumina composite ceramic substrate suitable for semiconductor devices has been invented. It is manufactured by a procedure starting with mixing powder formula of alumina, zirconia, and a self-made synthetic additive for ball milling in an organic solvent at room temperature. The resulting mixture is homogenously dispersed and is then subjected to the steps of slurry preparation, degassing, green embryo forming, punching, calculation, and sintering to yield the final composite ceramic substrate with an excellent mechanical property of three-point bending strength&gt;600 MPa and superior thermoelectric properties of thermal conductivity&gt;26 W/mK, insulation resistance&gt;1014 Ω·cm and surface leakage current (150° C.)&lt;200 nA.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a zirconia-alumina composite ceramic substrate for semiconductor devices and its manufacturing method; in particular, it refers to a procedure by mixing alumina, zirconia, and self-made synthetic additive powders to obtain the alumina-zirconium substrate with a mechanical property of three-point flexural strength>600 Mpa and thermoelectric properties of thermal conductivity>26 W/mK, insulation resistance>10¹⁴ Ω·cm, and low surface leakage current (150° C.)<200 nA.

Description of the Related Art

With the rapid development of electronic components, which substrates have clearly been required to become lighter, thinner, and shorter the long-time used alumina ceramic substrates, restricted by the mechanical strength characteristics, have gradually become unable to be satisfactory for practical uses.

A conventional alumina ceramic substrate is fabricated by sintering the alumina substances with a composition of alumina of 99.95% or higher purity and calcium oxide (Calcia) or magnesium oxide (Magnesia) of 100 ppm or less. However, following the development of thinning processes for large dimension devices, the mechanical strength of alumina ceramic substrates are evidently not enough to support subsequent operations such as sputtering, etching, and electroplating processes, or simply to meet the requirements for thinner components.

For a long time, alumina substrates have been widely used as insulating substrates for carrying semiconductor wafers, however, it can be considered that the demand for multi-operation semiconductors, semiconductor wafers often need to be charged with high voltage and high current, the traditional alumina substrates with lower mechanical strength and thermal conductivity are noted to not be beneficial for providing longer life time cycles, in particular, power module devices. Some manufacturers have proposed to dope certain kinds of additives such as zirconia and yttrium oxide to alumina and then the mixtures are sintered at high temperature, and they have claimed that the resulting substrate has a bending strength of 400 MPa. However, it is quite difficult for the substrate to achieve both high strength and high thermal conductivity at the same time. Usually, the high thermal conductivity substrate is obtained by grain growth of alumina sintered at higher temperature to reduce the grain boundary glass layer that causes thermal barriers. But, abnormal grain growth of alumina was accompanied with the higher sintering temperature, resulting in the drop of mechanical strength of alumina substrate.

In view of the above, the inventors have carried out a long-term research, and after numerous experiments, the invention has finally been produced.

SUMMARY OF THE INVENTION

The present invention aims to present a high-strength zirconia-alumina composite ceramic substrate suitable to be applied to semiconductor devices and its manufacturing method thereof, by mixing alumina (Al₂O₃), zirconia (ZrO₂) through a sintering aid (MCS) to form the zirconia-alumina composite ceramic substrate.

According to the high-strength zirconia-alumina composite ceramic substrate applied to semiconductor devices and its manufacturing method thereof the present invention, the obtained zirconia-alumina composite ceramic substrate includes a matrix phase formed by micrometer alumina particles, a reinforcement phase formed by submicron zirconia particles dispersed in the matrix phase, and a sintering additive synthesized in advance by calcination, and this is the next object of the present invention.

According to the high-strength zirconia-alumina composite ceramic substrate applied to semiconductor devices and its manufacturing method thereof the present invention, the zirconia particles dispersed in the matrix phase of alumina particles are composed of yttrium trioxide as a stabilizer in the crystalline phase of tetragonal zirconia, and this is another object of the present invention.

According to the high-strength zirconia-alumina composite ceramic substrate applied to semiconductor devices and its manufacturing method thereof the present invention, the sintering promotion additive is compounded from calcium oxide, silicon dioxide and magnesium oxide mixed in a certain ratio by bead milling and drying, and then synthesized silicon-magnesium-calcium compounds after calcination; by means of sintering additives to the zirconia-alumina composite ceramic material, the alumina particles shall contain a certain proportion of silicon-magnesium-calcium to lower zirconia-alumina composite ceramic sintering temperature and to improve the sintering microstructure uniformity, and this is another object of the present invention.

According to the high-strength zirconia-alumina composite ceramic substrate applied to semiconductor devices and its manufacturing method thereof the present invention, the obtained zirconia-alumina composite ceramic substrate have an excellent mechanical property of three-point bending strength>600 MPa and superior thermoelectric properties of thermal conductivity>26 W/mK, insulation resistance>10¹⁴ Ω·cm, and low surface leakage current (150° C.)<200 nA, and this is also another object of the present invention.

The detailed structure, application principles, functions and effects of the present invention, shall become completely understandable after referring to the following description made in accordance with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart for manufacturing the zirconia-alumina composite ceramic substrate of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

According to the high-strength zirconia-alumina composite ceramic substrate applied to semiconductor devices and its manufacturing method thereof the present invention, the produced zirconia-alumina composite ceramic substrate is made of alumina (Al₂O₃), zirconia (ZrO₂) and pre-synthesized sintering additives (MCS).

As shown in FIG. 1, the manufacturing process of the high-strength zirconia-alumina composite ceramic substrate applied to semiconductor devices and its manufacturing method thereof the present invention includes:

Ball milling step 100: Using alumina with a powder particle size (D50) of 0.70 to 3.0 μm, zirconia with a powder particle size (D50) of 0.20 to 0.80 μm, and pre-synthesized sintering additives of staring powder with a powder particle size of (D50) 0.30˜1.5 μm, is mixed with organic solvents by ball milling to achieve dispersion uniformly at room temperature;

Slurry preparing step 200: Preparing an alumina-based slurry by mixing alumina with addition of 1 to 15 wt. % zirconia and 0.01 to 5.0 wt. % a sintering promotion additives;

Degassing step 300: Degassing and defoaming the mixed slurry until the viscosity of the slurry reaches the pre-set range value of 8000˜30000 cps;

Green tape forming step 400: Forming a green tape roll with a thickness of 0.12 to 1.10 mm by tape casting the mixed slurry with a viscosity of 8000 to 30000 cps;

Punching step 500: Punching the zirconia-aluminum composite green tape roll into sheets of pre-set size;

Calculation step 600: The outside diameter of 227×168 mm of the green sheet is obtained by pre-testing the sintering shrinkage rate to calculate the size of the punched green sheet;

Sintering step 700: The green sheets of 227×168 mm size are fired at a temperature of 1560-1660° C. in a conventional continuous tunnel furnace to obtain the zirconia-alumina composite ceramic substrate having the size of 7.5 inches×5.5 inches and the thickness of 0.1-0.9 mm, preferably of 0.32 mm.

According to the high-strength zirconia-alumina composite ceramic substrate applied to semiconductor devices and its manufacturing method thereof the present invention, the obtained zirconia-alumina composite ceramic substrate includes a matrix phase formed by the micron alumina particles and the secondary phase formed the submicron zirconia particles dispersed on the matrix phase, and a sintering additive synthesized in advance by calcination. The matrix phase of alumina particles serves as the main phase, and the dispersed zirconia particles in the matrix are tetragonal zirconia crystals containing yttrium trioxide (Y₂O₃) as a stabilizer.

In the manufacturing process, the pre-synthesized additive is composed of calcium oxide, silicon dioxide and magnesium oxide in a certain proportion (for example, calcium oxide is 0.8˜8.8%, silicon dioxide is 56.7˜61.7%, and magnesium oxide is 32.5˜37.5%), is used as feedstock. The starting materials are mixed by bead mill and dried, and then the precursor is fired at a temperature of 850˜1250° C. to produce a silicon-magnesium-calcium oxide compound to ensure the less amount of 0.1 wt. % or more doping zirconia-alumina composite particles being surrounded with the certain proportion of silicon-magnesium-calcium oxides. Therefore, the function of pre-synthesized additive is noted to be beneficial for lowering sintering temperature for zirconia-alumina composite ceramics and enhancing the micro structural morphology uniformly.

According to the high-strength zirconia-alumina composite ceramic substrate applied to semiconductor devices and its manufacturing method thereof in the present invention, in the process for manufacturing the zirconia-alumina composite ceramic substrate, the self-prepared additive (MCS) can also be synthesized by combining calcium oxide, silica and magnesium oxide in a certain proportion by bead milling using zirconia beads as a mixing media. After mixing and drying, the powder mixture was obtained by calcining in furnace.

According to the high-strength zirconia-alumina composite ceramic substrate applied to a semiconductor devices and its manufacturing method thereof the present invention, the organic chemical binder comprises the solvent-based polyvinyl butyral (PVB), ether ester as the plasticizer, and an appropriate amount of surfactant as the dispersant.

MCS sintering Alumina Zirconia promotion additives (wt. %) (wt. %) (wt. %) Example 1 92.75 7 0.25 Example 2 91.25 8.5 0.25 Example 3 89.75 10 0.25 Example 4 89.75 10 0 Example 5 88.5 10 1.5

Three-point High temperature Apparent Bending Thermal surface leakage density strength conductivity current (gcm-3) (wt. %) (W/mK) (nA) Example 1 4.044 633 28.0 0.170 Example 2 4.064 649 28.1 0.169 Example 3 4.125 661 26.7 0.113

According to the high-strength zirconia-alumina composite ceramic substrate applied to semiconductor devices of the present invention, the less amount of silicon magnesium calcium sintering additives is uniformly dispersed among alumina particles by means of the pre-synthesized procedure. It is noted that the silicon-magnesium-calcium compound is helpful for lowering the sintering temperature to avoid abnormal grain growth of alumina, resulting a decrease in strength. Besides, alumina grain boundaries are surrounded by the excessive glass phases, thus giving a lower thermal conductivity. Therefore, it should be pointed out that the produced zirconia-alumina composite ceramic substrate with adequate amount of sintering additives and temperature shall have the following properties:

1. Excellent three-point bending strength>600 MPa mechanical properties.

2. Thermal conductivity>26 W/mK.

3. Insulation resistance>10¹⁴ Ω·cm.

4. Low surface leakage current (150° C.)<200 nA.

In summary, according to the high-strength zirconia-alumina composite ceramic substrate applied to semiconductor devices and its manufacturing method thereof the present invention, the characteristics of the zirconia-alumina composite ceramic substrate produced by the method are obviously superior than the traditional alumina ceramic substrate. The novel substrate is successfully satisfied with achieving the desired reliability for the post-substrate process operation and the required stability for the terminal devices. Therefore, the novel substrate along with its manufacturing method meet the conditions of the approvable patent.

The above description illustrates the preferred embodiment of the present invention. Any future alternative inventions as well as their effects deemed to be resulted from modifications of the above described invention should not be considered as new inventions, and thus the alternatives should belong to the present invention. 

What is claimed is:
 1. A method for manufacturing a high-strength zirconia-alumina composite ceramic substrate applied to semiconductor devices, comprising the following steps: Ball milling step: Mixing alumina, zirconia, and self-prepared additives respectively by ball milling using organic solvents as a mixing medium at room temperature; Slurry preparing step: Preparing an alumina-based slurry mix in combination with alumina/zirconia/sintering additive according to a predetermined mass ratio; Degassing step: Degassing and defoaming said slurry mix until the viscosity of the slurry mix reaches the pre-set range value; Green tape roll forming step: Obtaining a green tape of a predetermined thickness by tape casting. Punching step: Punching the zirconia-aluminum composite green tape roll into sheets of pre-set size; Calculation step: Calculating the dimensional size of said green sheet on basis of the pre-tested sintering shrinkage rate; Sintering step: Sintering said calculated green sheet into a zirconia-alumina composite ceramic substrate in a high-temperature furnace.
 2. The method for manufacturing a high-strength zirconia-alumina composite ceramic substrate applied to semiconductor devices as set forth in claim 1, wherein the powder particle size (D50) of the alumina is 0.7-3.0 μm; the powder particle size (D50) of zirconia is 0.2˜0.8 μm; the power particle size (D50) of the sintering additive is 0.3˜1.5 μm.
 3. The method for manufacturing a high-strength zirconia-alumina composite ceramic substrate applied to semiconductor devices as set forth in claim 1, wherein said slurry mix comprises the zirconia with a weight percentage of 1˜15 wt. %, the sintering additive with a weight percentage of 0.01˜5.0 wt. %, and the rest is alumina.
 4. The method for manufacturing a high-strength zirconia-alumina composite ceramic substrate applied to semiconductor devices as set forth in claim 3, wherein the viscosity of said slurry mix is 8000˜30000 cps.
 5. The method for manufacturing a high-strength zirconia-alumina composite ceramic substrate applied to semiconductor devices as set forth in claim 1, wherein the zirconia-alumina composite ceramic substrate is sintered from the green sheet with the size of 227×168 mm at a temperature of 1560˜1660° C., into the zirconia-alumina composite ceramic substrate with the size of 190.5×138 mm, and thickness of 0.1˜0.9 mm, preferably of 0.32 mm.
 6. The manufacturing method of a high-strength zirconia-alumina composite ceramic substrate applied to semiconductor devices as set forth in claim 1, wherein the obtained zirconia-alumina composite ceramic substrate includes matrix phase formed by micron alumina particles and the minor phase formed by submicron zirconia particles dispersed in the matrix phase and a sintering additive synthesized in advance; the matrix phase of alumina particles serve as the main phase, and the tetragonal crystalline zirconia particles dispersed in the matrix phase contain yttrium trioxide (Y₂O₃) as a stabilizer.
 7. The manufacturing method of a high-strength zirconia-alumina composite ceramic substrate applied to semiconductor devices as set forth in claim 1, wherein the pre-calcined synthetic sintering additive is composed of calcium oxide, silicon dioxide and magnesium oxide in a ratio of calcium oxide 0.8˜8.8%, silicon dioxide 56.7˜61.7%, and magnesium oxide 32.5˜37.5%; after the components are mixed by the bead mill and dried, the mixture is calcined to produce a silicon-magnesium-calcium compound to ensure the uniformity of the addition in the zirconia-alumina composite ceramics, making the surrounding of alumina particles contain a certain proportion of silicon-magnesium calcium to lower the sintering temperature of the zirconia-alumina composite ceramics and improve the sintering microstructure uniformity.
 8. The manufacturing method of a high-strength zirconia-alumina composite ceramic substrate applied to semiconductor devices as claimed in claim 1, wherein the added self-prepared additive (MCS) is synthesized by mixing calcium oxide, silica and magnesium oxide in a certain proportion with zirconia beads for bead milling dispersion mixing, and the uniformly dispersed slurry mix is subjected to oven drying and subsequent high temperature furnace calcination synthesis.
 9. The manufacturing method of a high-strength zirconia-alumina composite ceramic substrate applied to semiconductor devices as set forth in claim 1, wherein the slurry mix includes organic chemical binder comprising the solvent-based polyvinyl butyral (PVB), ether ester as the plasticizer, and an appropriate amount of surfactant as the dispersant.
 10. A method for manufacturing a high-strength zirconia-alumina composite ceramic substrate applied to a semiconductor devices, the manufacturing process includes: Ball milling step: Using alumina with a powder particle size (D50) of 0.7-0.3 μm, zirconia with a powder particle size (D50) of 0.20-0.80 μm, and pre-synthesized sintering additive with a powder size (D50) of 0.3˜1.5 μm as starting powders for ball milling mixing and dispersion in organic solvent at room temperature; Slurry preparing step: Preparing the alumina slurry mix with 1 to 15 wt. % of zirconia, 0.01 to 5.0 wt. % of sintering promotion additive and the rest of alumina; Degassing step: Degassing the slurry mix until the viscosity of the slurry mix reaches the pre-set range of 8000˜30000 cps; Green embryo forming step: The slurry mix with viscosity of 8000˜30000 cps is scraped to form a green embryo roll with a thickness of 0.12˜1.1 mm; Punching step: Punching the zirconia-aluminum composite green embryo roll; Calculation steps: Calculating the outer diameter of the green embryo based on the pre-tested sintering shrinkage rate to yield the punched green embryo with the size of 227×168 mm; Sintering step: Sintering said calculated green embryos with a size of 227×168 mm through a high-temperature furnace at a temperature of 1560˜1660° C. and heat them into the zirconia-alumina composite substrate with a size of 190.5×138 mm and a thickness of 0.1-0.9 mm.
 11. A method for manufacturing a high-strength zirconia-alumina composite ceramic substrate applied to semiconductor devices as set forth in claim 10, wherein the optimal thickness of the zirconia-alumina composite ceramic substrate obtained in the sintering step is 0.32 mm.
 12. A high-strength zirconia-alumina composite ceramic substrate applied to semiconductor devices which is produced according to a manufacturing method using of claim 1, and has a mechanical property of three-point bending strength>600 Mpa and thermoelectric properties of thermal conductivity>26 W/mK, insulation resistance>10¹⁴ Ω·cm and low surface leakage current (150° C.)<200 nA. 